FIELD OF THE INVENTION
The invention relates to a method of operating a printing machine, more particularly, a printing machine including an inking unit having a vibrator roller that swings reciprocatingly between an ink-duct roller and an inking-unit roller and has intermittent contact with these rollers. The invention also relates to a printing machine, and more particularly, to a printing machine having an inking unit including a vibrator roller that swings reciprocatingly between an ink-duct roller and an inking-unit roller and has intermittent contact with these rollers.
In sheet-fed offset printing machines, the ink for printing is provided via so-called vibrator inking units having an ink-duct roller that cooperates with an ink duct and a metering device. The thickness of the ink layer on the ink-duct roller can be adjusted by the metering device on the ink duct. By intermittent contact with the ink-duct roller, a vibrator roller removes a strip of ink of specific length from the ink-duct roller and, during subsequent contact with an inking-unit roller, transfers this quantity of ink to precisely this inking-unit roller. By additional inking-unit rollers following the last-mentioned inking-unit roller, a multiple splitting of the quantity of ink fed by the vibrator roller is effected, and by suitably provided ink-applicator rollers, appropriate inking of the printing regions of the printing plate located on a plate cylinder is performed. In order to have an influence upon the quantity of ink conveyed from the ink duct into the inking unit, it is possible for the metering device to be adjusted so that the ink layer thickness on the ink-duct roller varies. However, the ink layer thickness on the ink-duct roller must not fall below a specific minimum value, that may be set reproducibly, in a reliable manner.
The published Non-prosecuted German Patent Application (DE-OS)27 20 371 describes a device for driving a ductor or ink-duct roller for inking units of printing machines, in which the quantity of ink is varied as a result of suitably controlling the mutual phase angle of the movements of the vibrator roller and the ink-duct roller by adjusting the position of driving and driven elements of a nonuniform gear mechanism, so that the instant of time of the controlling step of the vibrator roller against the ink-duct roller changes. If the quantity of ink is to be reduced, the region in which the ink-duct roller is stationary is partly shifted into the region in which the vibrator roller makes contact with the ink-duct roller. In the extreme case, contact between the vibrator roller and the ink-duct roller may take place during the time in which the ink-duct roller is stationary, so that the quantity of ink that is picked up is virtually equal to zero.
Although it is possible for the quantity of ink conveyed into the inking unit to be reduced, when the foregoing device is used, the method upon which the device is based can be used only in the case of devices having an ink-duct roller that is driven discontinuously. The device for performing the method described in the aforementioned published German patent application is additionally very complicated in terms of construction.
The published German Patent Document DE 44 06 727C2 describes a method of controlling the supply of fluid during the production of printed products, in which, following the input of a command effecting a change in the speed of the printing machine, but before the speed change is executed, the rate of supply of the fluid is changed in accordance with a predefined time function and, following a preselected number of machine revolutions, the speed change of the main drive is initiated. This may be performed by initiating a speed change of an ink ductor before the speed change of the printing machine. The movement characteristic of the ink ductor is always maintained.
With this method, although an ink change on the printed material during the change of the printing speed can be avoided, it is not possible for any reliably reproducible minimum supply rate to be achieved.